/**
 * useReadingSettings — fetch and manage user reading preferences.
 * Applies settings as CSS custom properties on the document root.
 */

import { useCallback, useEffect, useState } from "react";
import {
  getReadingSettings,
  updateReadingSettings,
} from "../api/reader";
import type { ReadingSettings } from "../types/reader";

const DEFAULT_SETTINGS: ReadingSettings = {
  font_family: "serif",
  font_size: 18,
  line_height: 1.6,
  margin_width: 16,
  background_color: "#f5f0eb",
  text_color: "#1a1a1a",
  brightness: 100,
  orientation_lock: "auto",
  theme: "sepia",
  created_at: "",
  updated_at: "",
};

function applyCssVariables(settings: ReadingSettings): void {
  const root = document.documentElement;
  root.style.setProperty("--reader-bg", settings.background_color);
  root.style.setProperty("--reader-text", settings.text_color);
  root.style.setProperty("--reader-font-family", settings.font_family);
  root.style.setProperty("--reader-font-size", `${settings.font_size}px`);
  root.style.setProperty("--reader-line-height", String(settings.line_height));
  root.style.setProperty("--reader-margin", `${settings.margin_width}px`);
  root.style.setProperty("--reader-brightness", `${settings.brightness}%`);
}

export interface UseReadingSettingsReturn {
  settings: ReadingSettings;
  isLoading: boolean;
  error: string | null;
  updateSettings: (partial: Partial<ReadingSettings>) => Promise<void>;
}

export function useReadingSettings(): UseReadingSettingsReturn {
  const [settings, setSettings] = useState<ReadingSettings>(DEFAULT_SETTINGS);
  const [isLoading, setIsLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  // Fetch settings on mount
  useEffect(() => {
    let cancelled = false;
    setIsLoading(true);
    getReadingSettings()
      .then((data) => {
        if (!cancelled) {
          setSettings(data);
          applyCssVariables(data);
        }
      })
      .catch((err: unknown) => {
        if (!cancelled) {
          setError(
            err instanceof Error ? err.message : "Failed to load reading settings"
          );
          // Apply defaults
          applyCssVariables(DEFAULT_SETTINGS);
        }
      })
      .finally(() => {
        if (!cancelled) setIsLoading(false);
      });
    return () => {
      cancelled = true;
    };
  }, []);

  const updateSettings = useCallback(
    async (partial: Partial<ReadingSettings>) => {
      try {
        const updated = await updateReadingSettings(partial);
        setSettings(updated);
        applyCssVariables(updated);
        setError(null);
      } catch (err: unknown) {
        setError(
          err instanceof Error ? err.message : "Failed to update reading settings"
        );
        throw err;
      }
    },
    []
  );

  return { settings, isLoading, error, updateSettings };
}